In recent years, a fuel-cell electric vehicle and a hydrogen gas vehicle have become a focus of attention. The fuel-cell vehicle generates electricity by electrochemically causing hydrogen to react with oxygen in air, and generates driving force by supplying the generated electricity to a motor. The hydrogen gas vehicle includes an internal combustion engine that burns hydrogen gas instead of gasoline.
These vehicles are equipped with a tank for storing hydrogen gas (see, for example, Patent Document 1). When the remaining amount of hydrogen gas in the tank is small, hydrogen gas is charged into the tank at a hydrogen station as a fuel gas station.
A temperature sensor and a pressure sensor are installed in the tank, and the amount of hydrogen gas filled in the tank is allowed to be acquired from an indicated value of the temperature sensor and an indicated value of the pressure sensor. With the temperature sensor, it is possible to perform temperature management so that the temperature in the tank does not exceed a limit value. The temperature in the tank increases as hydrogen gas is charged.
As for the above-described temperature management, there has been suggested that temperature information in a tank is sequentially transmitted from a vehicle side to a hydrogen station side and the hydrogen station automatically stops charging of hydrogen before the temperature of the tank exceeds its permissible temperature (see, for example, Patent Document 2).
However, if the temperature sensor in the tank has an abnormality due to a drift, or the like, the following problems arise because it is not possible to accurately measure the temperature in the tank.
Initially, the problem in the case where the temperature sensor indicates a temperature higher than an actual temperature in the tank as an indicated value will be described. For example, it is assumed that, when an environmental temperature (ambient temperature) is −40° C. and the actual temperature in the tank is also −40° C. as well as the environmental temperature, the indicated value of the temperature sensor is 85° C. (that is, there is a drift of +125° C. in the temperature sensor). The hydrogen station feeds hydrogen gas to the tank by adjusting the feeding rate (pressure) of hydrogen gas so that the indicated value of the temperature sensor does not increase to 85° C. or higher.
In this case, hydrogen gas is charged into the tank until a filling pressure that is assumed in the case where the temperature in the tank is 85° C.; however, the actual temperature in the tank is −40° C., with the result that overcharging occurs (the filling factor becomes higher than or equal to 100%). In addition, if the vehicle moves to a place of which the environmental temperature is, for example, 65° C. after completion of charging, there is a concern that the temperature in the tank steeply increases and exceeds a permissible pressure of the tank.
Secondly, the problem in the case where the temperature sensor indicates a temperature lower than the actual temperature in the tank as an indicated value will be described. In this case, there is a possibility that hydrogen gas is charged even when the temperature in the tank exceeds 85° C. If hydrogen gas continues to be charged into the tank in such an overheating state (the temperature in the tank is higher than or equal to 85° C.), there is a concern of occurrence of troubles, such as a decrease in the strength of the tank resulting from thermal degradation of a resin portion of the tank and emission of hydrogen gas to the outside of the vehicle resulting from activation of a relief valve.
That is, if hydrogen gas is charged based on the indicated value of the temperature sensor in a state where there is a drift in the temperature sensor in the tank, overcharging or overheating occurs, with the result that stress larger than that in ordinary use acts on the tank.
Therefore, there has been suggested a fuel gas filling system in which a temperature difference between a temperature in a tank and a temperature of hydrogen gas that is fed to the tank is calculated, it is determined that temperature information in the tank is abnormal when the temperature difference exceeds a predetermined threshold Tth, and a flow rate of hydrogen gas that is fed to the tank is reduced as compared to during normal times (see, for example, Patent Document 3).